Salt bath refining

Abstract

A process for heating thermally unstable or difficult to heat liquid feeds, e.g., used lubricating oil (ULO) to dehydrate and/or recover distillable components therefrom, is disclosed. The liquid feed is heated by direct contact heat exchange with molten salt, preferably maintained as a bath, operating at a temperature above the boiling point of water and below 600 C. The liquid feed is heated and typically at least partially vaporized in, or above, or by contact with the molten salt to produce a heated liquid. When ULO contaminated with water is the feed, the vapor product of the process will comprise water vapor and/or distillable hydrocarbons. ULO additive decomposition products, such as carbon, may be removed as a solid, semi-solid or liquid residual phase from contact with the molten salt.

1. A method of refining used lubricating oil (ULO) containing lubricant boiling range hydrocarbons and thermally decomposable additives to recover as a hydrocarbon liquid product at least a portion of said lubricant boiling range hydrocarbons comprising:
 a. heating said ULO by direct contact heat exchange with molten salt having a temperature of 100° to 600° C. for a time sufficient to vaporize at least a portion of said lubricant boiling range hydrocarbons; 
 b. removing as a vapor product said lubricant boiling range hydrocarbons; and 
 c. recovering from contact with said molten salt a liquid residue product comprising said thermally decomposable additives or decomposition products thereof as a heavy liquid product. 
 
     
     
       2. The process of  claim 1  wherein said ULO contains distillable, lubricant boiling range hydrocarbons and non-distillable or thermally decomposable additives and said ULO is heated by direct contact heat exchange to a temperature of 100° to 400° C. and sufficient to vaporize at least a majority of said lubricant boiling range hydrocarbons and recovering said vaporized lubricant boiling range hydrocarbons as a product of the process. 
     
     
       3. The process of  claim 2  wherein said temperature and residence time are sufficient to decompose at least a majority of said decomposable additives and vaporize at least a majority of said lubricant boiling range hydrocarbons. 
     
     
       4. The process of  claim 1  wherein at least a majority of said ULO is recovered as a vapor fraction which is essentially free of motor oil additives and at least a majority of said additives, or decomposition products thereof, are recovered as a separate liquid phase from said molten salt. 
     
     
       5. The method of  claim 1  wherein said molten salt is maintained as a continuous phase. 
     
     
       6. The method of  claim 5  wherein said molten salt is disposed as one or more baths of molten salt and said ULO is injected into, or bubbles up through, said molten salt. 
     
     
       7. The method of  claim 1  wherein said ULO is maintained as a continuous phase and said molten salt is poured, sprayed or otherwise passed down through said continuous ULO phase. 
     
     
       8. The method of  claim 1  wherein 75 to 80 LV % of the feed is vaporized. 
     
     
       9. The process of  claim 1  wherein direct contact heat exchange occurs under vacuum. 
     
     
       10. A process for refining a used lubricating oil (ULO) liquid feed comprising water, lubricant boiling range hydrocarbons and non-distillable or thermally decomposable additives comprising:
 a. dehydrating said ULO in a dehydration stage by heating at a temperature and pressure sufficient to vaporize said water from said ULO and produce dehydrated ULO; 
 b. heating said dehydrated ULO by direct contact heat exchange with molten salt at a temperature and pressure sufficient to vaporize at least a majority of said lubricant boiling range hydrocarbons in said dehydrated ULO aid produce a vaporized lubricant boiling range hydrocarbon fraction and a residue liquid phase containing at least a majority of said non-distillable or thermally decomposable additives or decomposition products thereof; 
 c. cooling and condensing said vaporized lubricant boiling range hydrocarbons to produce a liquid product stream containing at least a majority of the lubricant boiling range hydrocarbons present in said ULO feed; and 
 d. removing said residue liquid from contact with said molten salt as a product of the process. 
 
     
     
       11. The process of  claim 10  wherein said molten salt is maintained as a continuous phase. 
     
     
       12. The process of  claim 10  wherein said molten salt has a temperature of 100° to 600° C. 
     
     
       13. The process of  claim 10  wherein direct contact heat exchange occurs at a pressure of 0.01 to 1.5 psia. 
     
     
       14. A process for distilling a used lubricating oil (ULO) liquid feed comprising lubricant boiling range hydrocarbons and a non-distillable residue fraction to produce two liquid product streams comprising:
 a. beating said ULO liquid feed by injecting said feed into a molten salt bath operating at a temperature of 580 to 800° F. and pressure of 0.01 to 1.5 psia, wherein said temperature and pressure are sufficient to vaporize at least a majority of said lubricant boiling range hydrocarbons present in said liquid ULO feed but vaporizing no more than 85 LV % of said ULO liquid feed and produce a vapor fraction comprising at least a majority of the lubricant boiling range hydrocarbons within said ULO liquid feed and a liquid phase residue comprising said non-distillable residue fraction; 
 b. removing from contact with said molten salt bath said vapor fraction as an overhead vapor stream; 
 c. cooling and condensing said overhead vapor steam to produce a first liquid phase product comprising at least a majority of said lubricant boiling range hydrocarbons in said ULO feed; and 
 d. removing from contact with said molten salt bath said liquid phase residue as a second liquid phase product. 
 
     
     
       15. A process for heating and partially vaporizing a thermally unstable liquid feedstock which cokes and/or rapidly fouls metal surfaces such as tubes in a fired heater, heat exchanger tubes, or the like, comprising:
 a. injecting liquid droplets of said thermally unstable feed into a non-pyrolyzing molten salt bath operating at a temperature of 100 to 500° C. and a pressure; 
 b. heating said injected droplets by direct contact heat exchange with said molten salt bath to a temperature, at the pressure in said bath, sufficient to vaporize at least a portion of said feed in each droplets and form bubbles rising up through said molten salt bath, each bubble having a vapor phase top and a residual liquid feed bottom in a molten salt shell; 
 c. heating said liquid in said bubble by direct contact heat exchange with said molten salt and heating said liquid by radiant heat transfer with said molten salt bath, to produce rising heated bubbles comprising heated liquid feedstock and vapor produced by heating said liquid feedstock to produce rising bubbles comprising a heated liquid phase and a vapor phase; 
 d. removing from above said molten salt bath said vapor phase as an overhead vapor product; and 
 e. removing from above said molten salt bath said heated liquid phase as a liquid phase product.